Synthetic reversible oxygen-binding iron chelates of different structures offer many potential applications both in gaining an understanding of ozygen binding itself and in biological studies. Both the chelates themselves and their possible degradation products will be subjected to testing in tisue culture, in small laboratry animals, and in organ perfusions. The fate and metabolism of these various compounds will be investigated both while in circulation and afterwards. Stroma-free hemoglobin will be used as a model compound in these experiments. This affords comparison between the advantages and disadvantages of the natural product and of the synthetic materials. The fact that hemoglbin in solution can be used for complete replacement of the blood of rats and thereafter maintain their lives proved that water soluble chelates can indeed be very valuable tools in biological systems.